Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A free falling drop sub carries an explosive tool such as a shaped charge
pipe cutter or well perforator. The drop sub includes an aperture
plugging element to isolate an upper pipe string from a lower pipe
string. An upper pipe string fluid pressure actuated valve element
retained by shear pins is released to admit the upper string pressure
against a pressure displaced firing pin. Displacement of the firing pin
initiates detonation of the explosive tool.

Claims:

1-32. (canceled)

33. A firing head for pyrotechnic well tools comprising: an axially
elongated tool body having an aperture plugging means for closing a
restrictive aperture within the bore of a pipe string; a fluid flow
conduit within said tool body for transfer of fluid through said tool
body to by-pass an aperture closed by said plugging means; axially
translated first piston means in said flow conduit having a first
position that obstructs fluid flow from a first port through said conduit
and a second position that enables fluid flow through said first port;
structural obstruction means for preventing the translation of said first
piston means in a first axial direction along said flow conduit from sad
first position; retaining means for preventing the translation of said
first piston means in a second axial direction along said flow conduit
from said first position, said retaining means releasing said first
piston to said second direction translation at a predetermined fluid
pressure on a first side of an aperture closed by said plugging means
whereby translation of said first piston in said second direction opens
said conduit to fluid flow in said first direction; and, firing pin means
for striking percussion ignition means to initiate a pyrotechnic well
tool, said firing pin means secured to said first piston means by
latching means, said latching means being released by translation of said
first piston means in said second direction.

34. A firing head as described by claim 33 wherein said latching means
comprises a second piston means having a first position for obstruction
fluid flow from said conduit through a second port and a second position
that enables fluid flow through said second port whereby translation of
said first piston means in said second direction releases said second
piston means to translate from said second piston first position to said
second piston second position.

35. A firing head as described by claim 33 wherein said retaining means
comprises at least one shear pin.

36. A firing head as described by claim 34 wherein said firing pin means
is carried by said second piston means.

[0002] The present invention relates to a system and method for
landing/positioning a device at a known depth within a pipe string
suspended within a wellbore without the use of e-line, wireline,
slickline or similar tether lowered from the surface. The present
invention is preferably utilized to position a downhole tool such as, for
example, a jet cutter, a shaped charge, a perforating gun,an explosive
charge, a perforating gun or well logging sensor in a tubing string for
purposes of pipe cutting, pipe perforation, formation perforation, pipe
recovery, well plugging, well logging or similar exercises. In one
embodiment, the invention relates to placement of explosive charges or a
jet cutter within a short section of easily and confidently severed pipe
that may be inserted at numerous locations in a pipe string at numerous
predetermined locations for separating an upper portion of a pipe string
from a lower portion at a precisely predetermined location. In another
embodiment, the invention relates to a well logging method that requires
no surface linkage during the survey.

SUMMARY OF THE INVENTION

[0003] The present invention system provides a series of internally
profiled seating subs which are distributed within a pipe string to form
a plurality of spaced apart pipe bore apertures immovably disposed along
the pipe string length. Each seating sub aperture is characterized by a
cross-sectional profile of varying shape with an aperture of a
predetermined diameter formed therein. The internally profiled seating
subs are arranged so that the aperture diameters decrease in regressive
increments as the pipe string extends deeper in a well bore. Utilized in
conjunction with these internally profiled seating subs is a sealing plug
of an external diameter selected to sealingly engage a specific one of
said profiled seating subs. The select diameter sealing plug is
configured to be secured to the exterior of a down hole tool assembly
that includes a service tool such as a firing head, shaped charge cutter,
perforating gun or stand alone well logging instrument to permit the tool
assembly to be landed on a seating aperture at a desired depth. The known
distance from the seating aperture to precisely where the service tool
functions in the pipe string is critical to the ability to predict what
service tool is best suited to achieving the desired result.

[0004] More specifically, an invention intent is to install these seating
subs at strategically determined points along the length of a pipe string
such as a drill string, drill pipe, drill collars, tubing, tubulars or
casing in a sequence that progresses from the largest diameter aperture
restriction to the smallest diameter aperture restriction. An independent
device carrying a plug profile of predetermined diametric dimension, when
dropped freely or pumped from the surface through the pipe string, will
pass through the pipe string until the device strikes a seating aperture
beyond which it cannot pass; e.g. a seating aperture diameter that is
smaller than the outer diameter of the plug. A metal-to-metal (or other)
seal will enable fluid pressure to be applied to the to the pipe string
bore above the seal for various purposes such as, for example, triggering
an explosive tool firing head and/or opening a by-pass valve and or
revealing the location of a logging tool. The type of device utilized in
the system can be any service tool utilized in downhole applications.

[0005] Although not intended to be limited for use with any particular
device, the system is particularly useful in pipe recovery operations
that may use service tools such as a jet cutter, severing tool, torch
cutter or chemical cutter. Other uses for the invention may also include
specific placement of perforating guns and well logging sensors.

[0006] An additional embodiment of the invention combines a restriction or
internally profiled seating sub as described above with a specially
designed cutaway sub. The combination of seating sub and cutaway sub may
be integrated with a pipe string at numerous, spaced, but carefully
measured locations along the pipe string length and especially above or
along the drill string weight collars. The cutaway sub includes a
sacrificial section having a reduced external diameter (reduced wall
thickness), relative the upper and lower coupling portions of the sub.
Utilizing an aperture profile positioned above the section of reduced
pipe wall annulus that is to be severed, the appropriate severing tool
(such as a jet cutter or shaped charge explosive) may be accurately and
confidently located to effect a clean cut. Significantly, once the cut is
made and the upper section of drill string is withdrawn, the severed end
of the reduced pipe wall annulus remaining with the lower end of the
drill string is easily accessed by conventional "fishing" technology
because the severed end is not excessively flared. This reduced wall
annulus section of pipe also facilitates perforating operations
previously made very difficult if not impossible by the thickness of the
drill collar. The tensile strength of a particular cutaway sub is
designed to be sufficient to support the pipe string below the particular
sub. This may be a variable value since those cutaway subs near the lower
end of a pipe string support less pipe weight below them than those
cutaway subs near the surface or top of a pipe string which must support
the weight of the entire string below.

[0007] A sleeve or bushing may be installed over the reduced wall annulus
section of the severing sub to ensure that the buckling and torsional
strength threshold of the sub is maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The advantages and further features of the invention will be
readily appreciated by those of ordinary skill in the art as the same
becomes better understood by reference to the following detailed
description when considered in conjunction with the accompanying drawings
in which like reference characters designate like or similar elements
throughout.

[0009] FIG. 1A illustrates a section of pipe string having two sub units
of the invention inserted between a upper pipe section and a lower pipe
section.

[0010] FIG. 1B is a sectioned view of FIG. 1A showing a drop assembly
within the pipe string in pipe cutting position.

[0011] FIG. 1C is a sectioned view of FIG. 1A showing the discharge of a
jet cutting tool against a reduced wall annulus section of the
sacrificial mandrel.

[0012] FIG. 1D is a sectioned view of the severed pipe section of FIG. 1C
showing withdrawal of the upper pipe section from the severed lower pipe
section.

[0013] FIG. 1E is a sectioned view of the severed pipe stub remaining
below the cut of FIG. 1C.

[0014] FIG. 1F is a full profile view of the severed stub remainder of the
pipe section.

[0015] FIG. 2 portrays the cross-section of a pipe string with a series of
seating apertures disposed therein to form decreasing restrictions along
the length of the pipe string.

[0017]FIG. 3A is an enlarged, partially sectioned view of the drop
assembly along the top section A of FIG. 3.

[0018] FIG. 3B is an enlarged, partially sectioned view of the drop
assembly along the mid-section B of FIG. 3.

[0019]FIG. 3c is an enlarged, partially sectioned view of the drop
assembly along the bottom section C of FIG. 3.

[0020]FIG. 4 is an enlarged sectioned view of the present invention
firing head.

[0021] FIG. 5 is an exploded view of a preferred cutaway sub embodiment.

[0022] FIG. 5A-A is a cross-section view of the seating sub at cutting
plane A-A of FIG. 5

[0023]FIG. 6 is a sectioned view of the preferred cutaway sub embodiment.

[0024]FIG. 7 is an exploded view of an alternative cutaway sub
embodiment.

[0025]FIG. 8 is a sectioned view of the FIG. 7 cutaway sub embodiment.

[0026]FIG. 9 is a sectioned view of an alternative sacrificial mandrel
embodiment.

[0027] FIG. 10 is a sectioned view of a second alternative cutaway sub
embodiment.

[0028] FIG. 11 is a sectioned view of an alternative invention
application.

[0029] FIG. 12 is a partially sectioned view of a well logging application
of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] As used herein, the terms "up" and "down", "upper" and "lower",
"above" and "below" and other like terms indicating relative positions
above or below a given point of element are used in the description to
more clearly describe some embodiments of the invention. However, when
applied to equipment and methods for use in wells that are deviated or
horizontal, such terms may refer to a left to right, right to left or
other relationship as appropriate. Moreover, in the specification and
appended claims, the terms "pipe", "tube", "tubular", "casing", "liner"
and/or other tubular goods are to be interpreted and defined generically
to mean any and all of such elements without limitation of industry
usage.

[0031] The basic sequence of the present invention, as practiced, for
example, upon a drill string cutting operation, is represented by the six
view, A-F of FIG. 1. The FIG. 1A view shows an assembly of the basic
invention components in a downhole pipe string between an upper section
10 and a lower section 16. An expanded description of each of these
constituent components will follow hereafter.

[0032] The FIG. 1A illustration is usually most relevant to that
heavyweight section of drill pipe at the bottom end of a drill string
having joints of pipe with extremely thick wall annuli. To the well
driller's art, these pipe joints with exceptionally thick walls are known
as "drill collars". The invention seating sub 12 and cutaway sub 14 may
be positioned at the upper end of the collar section or at any
intermediate point or at numerous points below the upper end. However,
those of ordinary skill will understand that the principles described
herein with respect to drill collars are applicable to any form or
application of pipe or tube.

[0033] Referring to the sectioned view of FIG. 1B, an independent drop
assembly 22 is released at the surface to be driven by pump pressure or
to descend in free-fall along the pipe bore to terminate upon a plug
seating aperture 24 in the seating sub 12. A drop assembly extension 26,
usually extending below the seating aperture 24 is shown to support a jet
cutting pyrotechnic tool such as a thermite or shaped charge explosive
28. The extension 26 length is selected to place the jet cutter 28 within
the pipe bore opposite a thin wall section 30 of a sacrificial mandrel 20
portion of the cutaway sub 14.

[0034] FIG. 1B illustrates the drop assembly 22 as firmly resting upon
seating aperture 24. Fluid pressure within the upper pipe string bore is
increased to open a firing head valve disposed within the drop assembly
22. Opening the firing head valve initiates the jet cutter 28 ignition
sequence to discharge a high temperature cutting jet along cutting plane
29 against the thin wall section 30 of the sacrificial mandrel 20 as
represented by FIG. 1C.

[0035] With the thin wall section 30 of the sacrificial mandrel 20
severed, FIG. 1D shows the seating sub 12 and torque sleeve portions of
the upper pipe string 10 as free to separate from the sacrificial mandrel
stub 32 which remains fixed to the well bottom. FIG. 1E shows the
sacrificial mandrel stub 32 portion of the cutaway sub 14 in section as
remaining with the well bottom pending further, independent action of
recovery or well abandonment. FIG. 1F shows the mandrel stub 32 in full
profile.

[0036] Seating Sub

[0037] While FIG. 1 illustrates the invention in one particular
application and embodiment, FIG. 2 illustrates a greater and more generic
application wherein a series of seating subs 12 are distributed along the
length of the supported pipe string. The seating subs 12a, 12b, 12c, and
12d are internally profiled by plug seating apertures 24 of graduated
diameter "D" forming restrictions in the interior diameter of the subs.
The subs, positioned at measured locations in a pipe string 10 extending
from the surface 11 into a well bore 19, are arranged so that the largest
diameter profile or restriction is nearest to the surface, with ever
decreasing (in diameter) profiles, such that the deepest/lowest sub in
the string has the smallest diameter profile or restriction. For example,
in FIG. 2, seating aperture 24a of sub 12a, nearest the surface 11, has
the largest diameter Da restriction, while aperture 24d of sub 12d,
deepest in wellbore 19, has the smallest diameter Dd restriction.
The consecutive diameters Da, Db, Dc, and Dd decrease
with depth along wellbore 19. In any event, the seating apertures 24 are
disposed to engage the sealing plug 34 (shown in FIG. 3) of the drop
assembly 22.

[0038] In one preferred embodiment, the seating subs 12 are only
approximately two feet long and can be readily threaded or inserted into
a pipe string during make-up. In one embodiment of the invention, up to
five seating subs 12 are provided and arranged so that the effective
restriction diameter between consecutive subs decreases from the first
sub (nearest the surface) to the last sub (deepest in the wellbore) in
the pipe string. In other embodiments of the invention, at least fifty
seating subs 12 may be provided and arranged so that the effective
restriction diameter between consecutive subs decreases from the first
sub (nearest the surface) to the last sub (deepest in the wellbore) in
the pipe string. In the course of such pipe string make-up, records will
be made of the number of standard pipe joints or drill collars between
each seating sub 12. Hence, the distance from the top end of the pipe
string to each seating aperture is a measured value. Of course, the
number of seating subs and restrictions will depend on the length of the
overall pipe string and the diameter of the pipe in which restriction are
formed.

[0039] While the seating aperture 24 may take any shape, in the preferred
embodiment, the apertures are formed of a lip or flange symmetrically
disposed around the interior 42 of a seating sub 12, thereby forming an
immovable opening that is axially fixed and aligned relative to the
internal bore of the seating sub. Preferably, this seating aperture is
formed with a continuous, fluid sealing face 44. However, those skilled
in the art will appreciate that for certain applications that do not
require a fluid tight seal, the seating aperture 24 need not extend fully
around the interior of the seating sub 12 so long as a resulting aperture
is formed to function as a restriction, thereby creating a seat on which
an object can land. Nor does the aperture need to be symmetrical or
axially aligned relative to the pipe sub, so long as the overall system
comprises apertures of varying size arranged in consecutive order as
described herein. For example, the seating aperture 24 may take the form
of one or more tabs, fingers or projections extending into the bore of a
pipe sub so as to form a "restriction" therein.

[0040] In one preferred embodiment, the seating aperture 24 has an upper
sealing surface 44 and lower surface 46. The upper surface 44 is
contoured so as to engage an object provided with a similarly contoured
profile, thereby permitting a seal to be formed between the object and
the sealing surface when the object is seated on the upper surface 44. In
the example of FIG. 2, upper surface 44 is curved to form a concave
profile and disposed to receive an object with a correspondingly rounded
or tapered shape (such as is shown on drop assembly 22 of FIG. 3). Once
an object is seated, a seal is formed between the object and the sealing
surface 44 as pressure is applied to the object by the fluid column above
the object or otherwise by downwardly pumped fluid to the extent the
object is disposed to pass fluid therethrough. In one example, if the
object is connected to a explosive device, pressure from the surface
applied to the upper end of the explosive device not only maintains the
seal as described but may also be utilized to activate the explosive
charge below the seal.

[0041] Drop Assembly:

[0042] The drop assembly 22 illustrated by FIG. 3 is a preferred
configuration for a tool, device or object that may be conveyed in a pipe
string and externally shaped for landing on and engaging the seating
aperture 24. One intent of the invention is to provide a universal tool
body adapted to receive a specifically sized sealing plug element 34
secured to the exterior of the tool body. A variety of standard downhole
devices or service tools attached to the tool body, usually below the
sealing plug, provide flexibility in the system for use with whatever
tool and for whatever purpose is desired. Thus, in one embodiment of the
invention, sealing plug 34 may be integrally formed as part of the device
with which it is utilized, while in another embodiment of the invention,
sealing plug 34 may be secured to the exterior of such device as an
independent attachment

[0043] The basic elements of the drop assembly 22 are shown by the
enlarged sections of FIGS. 3A, 3B, and 3C which correspond to segments A,
B and C of FIG. 3. With respect to FIG. 3A, a fishing head 50 may be
provided at the upper end of the assembly 22 for independent tool descent
or removal from the pipe string when desired. The anticipated normal use
of the drop assembly 22 is a free release of the assembly at the surface
11 into the pipe string bore for pumped displacement or free-fall until
the sealing plug 34 engages the seating aperture 24. To control the rate
of assembly descent, one or more units of swab cups 52 are provided to
restrict the flow rate of standing bore fluid past the assembly as it
descends. If pumped down the pipe bore, the swab cups 52 provide a ring
seal between the assembly 22 and the pipe bore wall to increase the
operational area of the upper pressurized fluid upon the assembly 22.
Additional to the swab cups 52 are one or more resilient centralizers 54
to keep the assembly aligned with the pipe string axis during the
descent. Although there are many pipe centralizer configurations. the
present embodiment provides three spring blades 56 secured to a carrier
tube 58. Apertures 59 in the carrier tube wall allow pressure
equalization between the carrier tube interior and the surrounding pipe
string bore.

[0044] FIGS. 3B and 3C collectively illustrate the drop assembly firing
head 60 which is also shown in enlarged section by FIG. 4. Central to the
firing head 60 is a release valve mechanism comprising a differential
area piston 62 that is initially held against an annular ledge as a
bottom seat 64 in a bore sleeve by shear pins 65. The piston 62 upper
diameter 67 is greater than the diameter 68 below the fluid port 66.
Displacement of the piston 62 from an initial, port 66 closing position
may only occur in an upward direction into a blind bore 70 by pressure
differentially shearing pins 65. Accordingly, the piston 62 is positively
caged from accidental or shock release as it descends along the pipe
string bore.

[0045] The sleeve 63 is threaded onto a tube extension 70 below the swab
cup 52. Tube extension 70 includes a blind bore 71 of substantially the
same inside diameter as the large diameter 67 of the piston 62.

[0046] A reduced diameter pintle 72 projects from the lower face of piston
62 into the bore 74 of a fluid transfer tube 73. the upper end of the
transfer tube is perforated by a plurality of biased angle apertures 75.
Each of the apertures 75 contains a latching ball 76 which has
substantially the same diameter as the annulus thickness that is the
differential between the pintle 72 radius and radius of the counterbore
77 in the bore sleeve 63.

[0047] For the preferred embodiment, the transfer tube 73 extends through
an axial bore 77 in the sealing plug 34 into a release sleeve 78. A fluid
flow annulus is provided between the outer perimeter of the transfer tube
73 and the inside wall of the sealing plug bore 77.

[0048] At the release sleeve end of the transfer tube 73, the transfer
tube 73 is given an enlarged outside diameter 79 for a sliding, O-ring
seal fit within a release sleeve bore restriction 122 between annular
chambers 123 and 124. The lower chamber 124 is ported by apertures 126
into the surrounding pipe string annulus

[0049] A firing pin housing tube 128 is threaded into the release sleeve
78 (FIG. 4). The upper end of firing pin 130 is seated within the lower
end of the transfer tube bore 74 with an O-ring fluid seal. The lower
distal end 131 of the transfer tube engages a perimeter shoulder on the
pin 130 to limit penetration of the pin 130 into the transfer tube bore
74. The outside perimeter of the transfer tube 74 lower end is given and
0-ring fluid seal fit within the housing tube bore. The up end 137 (FIG.
3C) of a linking tube 138 between a tool coupling 134 and the lower end
of the housing tube 128 provides a travel limit shoulder for the transfer
tube 73 and hence, the firing pin 130. For the purpose of a pyrotechnic
tool such as a jet or shaped charge tubing cutter, a percussion activated
explosive initiator 135 will be secured in the tool coupling 134. The
stroke of the transfer tube 73 along the housing tube bore 132 is
designed to bring the firing pin 130 striker point 139 into physical
contact with the percussive initiator 135.

[0050] In most applications, plug 34 engagement of a predetermined seating
aperture 24 will isolate the pipe string bore into an upper fluid
pressure zone above the seating aperture 24 and a lower pressure zone
below the seating aperture 24. The pressure in the upper zone at the
seating aperture 24 is determined by the fluid head standing above the
seating aperture 24 and any externally applied pump pressure. Pressure in
the pipe string bore below the seating aperture 24 is usually determined
by multiple factors such as the standing fluid head in the wellbore
annulus, the presence of well packers, and the in situ bottom hole well
pressure.

[0051] To trigger the firing pin against the explosive initiator 135,
fluid pressure in the upstream pipe bore is raised by pump pressure to
exceed that of below the seating aperture by a sufficient differential to
shear the pins 65. Upper pipe bore fluid pressure enters the drop
assembly through ports 66 to bear against the differential area piston
62. Due to the dimensional difference between the large diameter 67 end
of the piston and smaller diameter end 68, a net shear force on the
piston 62 is borne by the shear pins 65. When the pins 65 fail under this
differential area force, the piston 62 is driven upward into the blind
bore 71 of extension tube 70. When the piston 62 enters the blind bore
71, the pintle 72 is extracted from the upper bore end of transfer tube
73. Resultantly, the latching balls 76 are released into the bore 74 of
transfer tube 73.

[0052] When the differential area piston 62 shifts upward into the blind
bore 71, pressurized fluid in the upper pipe string bore also enters the
inner chamber of the bore sleeve 63 to bear against the transfer tube 73
cross-section. The force of such cross-sectionally applied fluid pressure
drives the transfer tube 73 downward along the sealing plug bore 77 and
firing pin striker point 139 against the explosive initiator 135.
Simultaneously, the enlarged diameter section 79 of the transfer tube 73
is shifted downwardly from sealing contact with the release sleeve bore
restriction 122. The latter shift permits fluid flow from the upper pipe
string segment to pass through the port 66 into the flow annulus between
the transfer tube 73 and sealing plug bore 77 and out the release sleeve
aperture 126 thereby bypassing the pipe string bore seal at the plug
seating aperture 24.

[0053] This fluid by-pass opening between ports 66 and 126 allows the drop
assembly and any attached tool to be withdrawn from the pipe string by a
wireline connected to the drop assembly fishing neck 50. As the drop
assembly 22 is lifted, the by-pass opening allows fluid in the pipe
string bore to drain past the drop assembly into the pipe string bore
below the drop assembly.

[0054] Cutaway Sub

[0055] The foregoing description has been of a system for precisely
placing a specialty tool along the length of a pipe string bore. Among
the numerous downhole operations receiving advantage from such
positioning accuracy is that of pipe cutting. There are occasions when it
is advantageous to sever a pipe string downhole and withdraw the upstring
portion. The severed lower portion of the pipe string may be either
abandoned in place or, as the usual case, recovered by one of numerous
"fishing" techniques. When the objective is to sever a drill pipe, care
is taken to place the cutting tool at a point along the pipe length
between the pipe coupling joints. Pipe coupling joints normally have a
considerably greater wall thickness than the nominal wall of the pipe.
The thinner wall thickness of the nominal pipe wall is more easily
severed with a `clean` cut face without flash, burrs or flare which may
interfere with extraction of either the severed, uphole string or of the
downhole string.

[0056] Drill collars, however, are a special case wherein the outside
diameter of a pipe joint is the same as the coupling diameter along the
entire joint length. The functional purpose of such a configuration is
for ballast weight at the bottom end of the drill string. Moreover, when
a pipe string becomes `stuck" in a borehole in progress, it is frequently
due to bore wall sloughing into the bore annulus around the drill
collars. Hence arises the occasional necessity to sever the drill collar
string mid-length. It is for this task, that the combination of the
seating sub 12 as described above with a cutaway sub 14 is particularly
useful. With respect to FIG. 1, for example, the seating sub 12 and
cutaway sub 14 are positioned between upper and lower drill collars 10
and 16, respectively. Depending on the length of the drill collar
assembly there may be a plurality of seating sub and cutaway sub
combinations distributed along the drill collar segment of the pipe
string.

[0057] Turning to the exploded view of FIG. 5 and cross-sectional views of
FIGS. 5A-A and 6, one preferred embodiment of a cutaway sub 14 is shown
to include a sacrificial mandrel 20 having male threaded end-pins 140 at
both ends. Axially adjacent the end-pins are stepped bosses 142 and 144.
between the two stepped bosses 142 and 144 is a relatively thin wall tube
section 30 having an outside diameter that is substantially less than the
nominal drill pipe or collar diameter. The upper (smaller) stepped
portion 146 of boss 142 adjacent the threads 140 is formed with chordal
wrench flats corresponding to the wrench flats 149 in the torque sleeve
collar 147 shown by FIG. 5A-A. The number of wrench flats 149 is shown on
the inside perimeter of the sleeve collar 147 are only a representative
example. Those of ordinary skill will understand the collar 147 and boss
step 146 may be given as many flats as required to transfer the forces
necessary for rotatively driving the drill string below the seating sub
12.

[0058] The greater outside diameter section of stepped boss 142 is
dimensioned to receive the inside diameter of torque sleeve 18 with a
slip-fit overlay.

[0059] The smaller; outside diameter section 150 of lower boss 144 also is
preferably given a value corresponding to a slip fit overlay of the
torque sleeve 18. The larger diameter section 152 of the lower boss 144
may be essentially the same diameter as the drill collars 10 or 16. The
shoulder 153 between the two sections is cut with an undulating profile
such as the lug socket profile 154 for meshing with a corresponding lug
socket profile 156 in the end of torque sleeve 18.

[0060] It will be understood that the rotary torque transfer function
accomplished by the meshed wrench flats 149 in the torque sleeve collar
147 and the mandrel boss 146 may also be served by a multiplicity of
meshing splines. In either case, the sleeve 18 is assembled with the
mandrel 20 by an axially sliding fit to mesh the sleeve lug profiles 156
with the corresponding profiles 154 in the mandrel boss 144.
Simultaneously, the wrench flats 149 mesh with corresponding flats on the
mandrel boss 142. When the mandrel threads 140 are meshed with
corresponding threads in the seating sub 12, the torque sleeve 18 is
firmly secured against the upper mandrel boss shoulder 146 and the
dominance of all torsional stress transferred by the seating sub 12 to
the sacrificial mandrel 20 is carried by the torque sleeve 18.

[0061] As previously described, numerous sub-sets of seating subs 12 and
cutaway subs 14 may be distributed along the pipe string additional to
those among the drill collars. When an occasion arises to sever the pipe
string at a specific point, the drop assembly 22 is equipped with the
sealing plug 34 corresponding to the assigned seating aperture 24 that is
most proximate above the point of desired string separation. The pipe
cutting tool, also secured to the drop assembly, is positioned below the
sealing plug 34 at the same, precisely known distance as is the center of
the thinwall section If sacrificial mandrel 20 below the seating aperture
24. Hence, when the drop assembly 22 settles upon the seating aperture
24, it is known with confidence, that cutting tool is correctly
positioned relative to the sacrificial mandrel 20.

[0062] It is also known, with confidence, that the drop assembly 22 has,
in fact, settled against the designated seating aperture 24 by the fluid
pressure rise within the pipe string bore against a surface pump supply.
As the drop assembly descends the pipe string. The pipe bore pressure
remains at circulation pressure. When the sealing plug 34 settles against
the seating aperture 24, circulation is terminated and bore pressure
abruptly rises against the firing head 60. This pressure rise will
continue until the shear pin 65 rupture pressure is achieved to shift the
differential area piston 62 upwardly off the bottom seat 64 and release
the latching balls 76. When the latching balls fall into the transfer
tube bore 74, the transfer tube 73 shifts downwardly to open the upstream
fluid port 66 to flow communication with downstream fluid flow port 126.
When flow communication is established between fluid ports 66 and 126,
the bore pressure abruptly drops to the circulation pressure.
Consequently, when the pipe string pressure abruptly spikes and then
falls, it may be known that the drop assembly 22 has settled on the
seating aperture 24, the firing head has opened, the firing pin as fallen
and the pipe cutter 28 or perforating gun has discharged.

[0063] In the usual course of operations, after discharge of the cutter
28, the upper pipe string is withdrawn from the wellbore along with the
seating sub 12, the torque sleeve 18 and the upper portion of the
sacrificial mandrel 20 including the upper boss 142. Of the original
cutaway sub 14, only the lower boss 144 and lower pipe string remain in
the wellbore subject to abandonment or further retrieval operations.

[0064] An alternative embodiment 80 of the cutaway sub with increased
buckling strength is represented by FIGS. 7 and 8 as having a reduced
wall thickness tube 81 between stepped bosses 84 and 85. The upper end of
the reduced wall tube 81 is terminated by an interior portion of the
upper stepped boss 84. The lower end of the tube 81 is terminated by the
interior portion of the lower stepped boss 85. Both interior boss
portions are of greater outside diameter than the reduced wall tube 81.
At an axial set-back in opposite directions are an intermediate pair of
stepped bosses 86 and 87 having a greater OD than the interior bosses 84
and 85. The abutment transition between the interior and intermediate
bosses is profiled with lug detents 92. Meshing with the lug detents 92
are the lug projections 91 at opposite distal ends of a split sleeve 90.
There may be a plurality of such meshing lug projection 91 and detents
92.

[0065] The internal bore 101 of torque sleeve 100 is sized to pass freely
but closely with a slip fit over the intermediate bosses 86 and 87. Lug
102 on the lower end of sleeve 100 are sized and configured to mesh with
the lug detents 94 in the lower pin collar 88. Referring to FIG. 8, an
inside abutment face 104 of end collar 103 is positioned at the distal
end of sleeve bore 101 to engage a mating abutment face on the
intermediate stepped boss 86 as the sleeve lugs 102 mesh with the collar
detents 94. Internal wrench flats on the upper stepped boss 96 as
described for FIG. 5A-A are sized and configured to mesh with mating
wrench flats (not shown) on the interior perimeter of the sleeve 100 end
collar 103.

[0066] A seating sub 106 may be constructed with tapered box threads 107
and 108 at opposite ends. When the tapered threads 82 and 108 are in full
engagement, the inside abutment faces of the sleeve collar 104 and
intermediate boss 86 are in compressed juxtaposition.

[0067] Those of skill in the art will appreciate the operative consequence
of the FIGS. 7 and 8 assembly as not only stiffening the cutaway sub 80
but is also capable of transferring drive torque across the cutaway sub
80 through both inner and outer sleeves as well as the thinwall tube 81.
However, when the thinwall tube 81 is severed, the upper pipe string
maintains firm assembly with the sleeve 100 and upper stepped boss
elements of the sub 80 for withdrawal from the borehole. When the sleeve
100 is withdrawn. The split sleeve 90 halves have no radial confinement
and merely fall away form the severed lower portion of the sub.

[0068] In some cases, even the release of the split sleeve halves 90 as
borehole debris is intolerable or extremely expensive for a follow-up
fishing trip to remove the resulting debris. Responsive to those
applications. A third embodiment of the invention as represented by FIGS.
9 and 10 is suggested wherein the inner step 84 of the upper boss is
grooved with a perimeter encircling channel 114. The substantially
cylindrical surfaces of both inner steps 84 and 85 may be cut with wrench
flats 110 and 112.

[0069] A further modification of the FIGS. 9 and 10 embodiment may include
lug and detent engagements of the split sleeve 119 at the lower end as
suggested for the FIGS. 7 and 8 embodiment. In either case, whether by
lug and detent or by wrench flats, drive torque is transferred from the
top seating sub 106 to the lower pin 83 through the additional structure
of inner split sleeve 81 and torque sleeve 100.

[0070] Those skilled in the art will appreciate that the system described
herein provides certainty as to the depth of a tool in a pipe string.
Once a drop assembly has landed on a seating aperture 24 and the pipe
string pressure is raised against the shear pins 65 to be abruptly
released, the drop assembly is known to be on the designated seating
aperture and the exact position of a tool attached to the drop assembly
relative to the seating aperture is also known.

[0071] FIGS. 11 and 12 illustrate an alternative embodiment of a drop
assembly configured for placement of a non-explosive tool such as a
battery powered well logging sensor for detecting certain geologic
characteristics of the earth where penetrated by the wellbore.
Distinctively, the transfer tube 73 element of the drop assembly needs no
firing pin. Consequently, the distal end of the transfer tube 73 is
closed with an end plug 157. The firing head 60 becomes a one-time
pressure actuated release valve. The housing tube 128 becomes an
extension to which a battery pack 164, a data recorder 162 and well
logging sensor 160 are attached. The seating aperture 24 is positioned
within the seating sub 12 to allow at least the sensor 160 end to extend
beyond the open end 25 of the seating sub.

[0072] When a free falling drop assembly, for example, carries sensitive
instrumentation such as well logging sensors, it may be prudent to finish
the internal bore of the seating sub 12 for an extended distance above
the seating aperture 24 to more closely interact with the swab cups 52 to
slow the drop assembly descent before engaging the seating aperture 24.

[0073] The total length of the pipe string, including the distal end 25 of
the seating sub 12 and the position of the sensor 160 relative to the
seating aperture 24 will be known. When pump pressure shears the pins 65
and a pump pressure spike is suddenly released, it is known, with
confidence, exactly where the sensor 160 is located within the wellbore
19. If the data recorder 162 operates continuously, the well may be
logged continuously from the known position as the supporting pipe string
is withdrawn with the logging tool attached. It will be recalled that the
firing head by-pass valve is open therefore permitting standing pipe bore
fluid above the seating aperture 24 to by-pass the seal and equalize the
fluid pressure as the pipe string rises.

[0074] An additional benefit of the system is that a symmetrically
disposed seating aperture within a pipe bore allows tools positioned with
the system to be centralized in a pipe string resulting in substantially
improved performance of the explosives relating to the pipe recovery
system.

[0075] While the system of the invention is best utilized in the context
of a vertical wellbore, those skilled in the art will understand that the
invention may also be utilized in other elongated tubing sections where a
fluid is pumped through the tube and an operation at a precise distance
into the tube is required, including without limitation, horizontal
wellbores, sewer lines, pipe lines and the like.

[0076] Likewise, while the system preferably eliminates the need for
e-line, wireline, slickline or similar vehicles as a method for placement
of a device, the system may still be utilized in conjunction with such
vehicles to control the travel of such devices through the pipe string.

[0077] Although the invention disclosed herein has been describe in terms
of specified and presently preferred embodiments which are set forth in
detail, it should be understood that this is by illustration only and
that the invention is not necessarily limited thereto. Alternative
embodiments and operating techniques will become apparent to those of
ordinary skill in the art in view of the present disclosure. Accordingly,
modification of the invention are contemplated which may be made without
departing from the spirit of the claimed invention.